Further investigations regarding the development and analytical applications of new polymer membrane electrode-based gas sensing systems are proposed. These sensors will be fabricated by using various polymer membrane type ion-selective electrodes as internal sensing elements in static and automated gas sensing arrangements. A major part of this phase III research will involve examining the use of a new tubular gas sensing catheter for continuous in vivo measurements of pCO2. Efforts will focus on reducing the diameter of the current sensor and finding suitable coating materials to prevent in vivo thrombus formation. Attempts will also be made to utilize the existing pCO2 catheter design as the basis for developing a dual sensing pCO2/pIon catheter. This will be accomplished by incorporating appropriate ion carriers in the outer gas permeable silicone tubing of the pCO2 catheter, and simultaneously monitoring the membrane potentials of both the inner polymer pH electrode and the outer silicone rubber tube. The fabrication of enzyme-based catheters for in vivo monitoring of urea, creatinine, etc. will also be pursued. Actual in vivo evaluation of the various sensors to be developed will be conducted in collaboration with scientists in the Department of Anesthesiology at the University of Michigan Hospital. Aside from the catheter work, additional research efforts will be directed toward studying a new stop-flow/flow-injection arrangement for enhancing the sensitivity of automated polymer electrode-based gas detectors. This concept will be examined as an alternative approach for in vivo monitoring of pCO2 and NH3, as well as in the design of ambient NH3, NO2, and SO2 sensors. Finally, preliminary investigations will be undertaken to determine the feasibility of using certain lipophilic metallo- porphyrin species as anion binding reagents in anion selective polymer membrane electrodes. Emphasis will be placed on determining the mechanism of ion-association within the membranes (i.e., ion-exchange or neutral carrier) and on examining the prospects for achieving anion selectivity by sterically controlling the accessibility of axial coordination sites of the metal center. Anion electrodes of this type could prove useful in the development of improved CO2, NO2 and SO2 gas sensors.